Idiopathic polyneuritis or polyradiculoneuritis, otherwise known as Guillain-Barre syndrome, Landry's ascending paralysis, or Landry Guillain-Barre Strohl syndrome, is, since the advent of vaccination against polyomyelitis, the commonest cause of the acute severe generalized paralytic disease in man. Although a relatively common condition affecting the population at a reported annual prevalence of 1-1.6 cases per 100,000 population, it has recently come to immediate public attention in the United States as a presumed complication of vaccination against influenza (A/N J/76 - "swine flu"). By the study of the populations, including individuals with Guillain-Barre syndrome with or without swine flu immunization, the HLA complex, including serological antigens, mixed lymphocyte determinants and B cell antigens, immunological parameters which are known to be associated with the HLA complex, this proposal is designed to determine whether or not there are immunogenetic or immunological determinants which alone or in combination may define a population which is more likely to develop autoimmune neurological disease after influenza immunization.